The German researchers say the gene mutation they have found helped cause a particularly severe form of the mental illness - catatonic schizophrenia - in one large family.

They hope the discovery will help researchers get a better understanding of schizophrenia and how to treat it.

These discoveries, if proven, will probably not have a noticeable effect on people's quality of life for many years

Cliff Prior, chief executive of National Schizophrenia Fellowship

But mental health charities expressed fears that identifying the gene could lead to stigmatisation and discrimination.

A group of psychiatrists, geneticists and neuroscientists from the Department of Psychiatry and Psychotherapy at the Julius Maximilians-University in Wuerzburg found the gene during their investigation of chromosome 22.

They chose to study catatonic schizophrenia because the condition is known to be mainly inherited. Catatonic schizophrenia is characterised by acute psychotic episodes with hallucinations, delusions and disturbed body movements.

The researchers found that the gene, which they have called WKL1, produces a protein similar to those which play a crucial role in transmitting electric currents along the nerves.

Mutations in these proteins are also known to cause a rare movement disorder called episodic ataxia.

Better understanding

The scientists said the discovery of the WKL1 gene mutation, which is to be published in Molecular Psychiatry, should give them a better understanding of catatonic schizophrenia .

They found that a mutation in the gene showed up in seven family members with the disease, but not in six others who had no symptoms of schizophrenia.

One of the study's authors, Professor Peter Lesch, said they hoped their discovery would lead to the development of treatments for schizophrenia, which affects about 1% of the population.

He said: "I think hopefully it is educating the field a little better, although the step is a small one. But if this step can be confirmed, it would be a key player.

"We could then progress towards specific therapies."

But Professor Lesch said it was important to note that they were talking about the gene that could be responsible for just one specific type of schizophrenia and that there was much more work to be done.

Long wait

Cliff Prior, chief executive of the UK's National Schizophrenia Fellowship, said that although they welcomed the research, there were concerns that the findings could be abused to stigmatise schizophrenics.

He said: "Any progress towards understanding the nature of schizophrenia is welcomed.

"As with other recent genetic findings, there are some dangers as possession of a genetic marker might adversely affect an individual's opportunities in areas such as insurance, employment, housing and travel."

Mr Prior said that scientific discoveries often took some time to be put into practice.

"These discoveries, if proven, will probably not have a noticeable effect on people's quality of life for many years. In the meantime, there is a lot that can be done right now in terms of making current best practice treatments available to all."

Majorie Wallace, chief executive of mental health charity Sane, which founded the Prince of Wales' International Research Centre in Oxford to carry out studies of schizophrenia, said that because the German study traced only one family that the findings might be difficult to replicate.

"We are all involved in this search for a common gene and there have been many false dawns.

"Much more research is urgently needed before we can give hope of a revolution in treatment and an eventual cure to sufferers and their families."